2 PCS Wave Silicone Water Bottle Boot for Owala, Anti-Slip Protective Sleeve for FreeSip/Twist/Flip, Watter Bottle Accessories, Bottom Bumper Cover, Dishwasher Safe, BPA Free

I got one on Amazon thats perfect and was only $3 or so. It’s not “necessary” I guess but if you love your bottle, get one. Edit: this is the one I got. It’s now $6.99 for a set of 2 but I’ve been happy w my purchase. https://a.co/d/0aktuA4j